This invention generally relates to an ink jet recording method and an ink jet apparatus using the same. More specifically, this invention relates to an ink jet recording method utilizing vibration energy and an ink jet apparatus using the same.
On-demand type ink jet recording methods for jetting ink droplets on-demand from nozzles are well known. Recently, those ink jet recording methods are typically classified as piezoelectric-type or thermal-type. In the piezoelectric-type ink jet method, a pulse voltage is applied to a piezoelectric element that is located in an ink reservoir in order to deform the shape of the piezoelectric element for changing internal ink pressure thereof so that an ink droplet is jetted from a nozzle and a dot image is reproduced on a recording sheet. In thermal-type ink jet method, ink is heated by a heating element that is located in an ink reservoir for forming a bubble so that an ink droplet is jetted from a nozzle by the pressure of the generated bubble and a dot image is reproduced on a recording sheet.
In such ink jet recording techniques, resolution of reproduced dot images have typically been limited up to 300 dot per inch (dpi); however, recently, demands for increasing the image resolution up to 600 dpi, 720 dpi or more have been increased.
To comply with such demands and to perform such high-resolution recording, dot diameter to be recorded on a recording sheet should be decreased in accordance with such required resolution. In those aforementioned methods, nozzle diameter may be decreased in order to decrease the dot diameter. However, if the nozzle diameter is once decreased, nozzle clogging due to foreign matter or coagulation of ink material on an ink jetting surface or changing of ink jetting direction due to adherence of residue of the ink around the nozzle tend to occur. Therefore, there is an issue that such required nozzle diameter necessary to record a dot having a diameter corresponding to such resolution can not be utilized because the aforementioned nozzle or image defects occur.
Regardless of such proposals, recently, an ink jet recording method utilizing a surface acoustic wave has also been proposed. For example, an ink jet recording method for forming a surface acoustic wave by interdigital electrodes that are located in an ink reservoir and then vibrating the ink with a leaked Raley wave generated therefrom to jet the ink from a slit or nozzle is disclosed in Japanese unexamined patent publication (JP-A) 54-10731. Another ink jet recording method is also proposed in JP-A 62-66943, which comprises placing a concentrically-formed interdigital electrode at a bottom portion of the ink reservoir, forming leaked Raley waves and concentrating the waves conically and placing ink material so that the top of the cone is located near the surface of the ink material in order to concentrate the vibrating energy propagated in the ink at the ink surface and jet an ink droplet from the ink surface.
In those methods, since the diameter of the produced ink droplet is not directly affected by the nozzle diameter, it is not necessary to reduce the nozzle diameter as well as its shape independency. However, since the interdigital electrodes for generating the surface acoustic wave are located within the ink material, there are some issues that the electrodes are melted due to interaction generated by the high frequent vibration between the ink material and the electrodes or the ink material adheres on the electrodes. In addition, there is another issue that energy efficiency is relatively low because the leaked Raley waves are easily attenuated during the propagation thereof in the ink material.
In order to solve those issues, a new ink jet recording method utilizing the surface acoustic wave has been proposed in JP-A 2-269058. FIG. 14 is an explanatory view for explaining the principle of a conventional ink jet recording method using surface acoustic wave. In FIG. 14, 41 is a surface of a piezoelectric plate, 42 is an interdigital electrode, 43 is the piezoelectric plate, 44 is ink, 45 is an ink droplet and 46 is a high frequency power supply. The interdigital electrode 42 is formed on the surface of the piezoelectric plate 41. High Frequency electric voltage is applied to the interdigital electrode 42 from the high frequency power supply 46 and ink 44 is placed on a propagating path of the generated surface acoustic wave. When the surface acoustic wave contacts the ink 44, vibration energy leaks into the ink, i.e. generation of the leaked Raley wave, and a portion of the ink is jetted therefrom as an ink droplet 45. In this system, since ink 44 does not directly contact the interdigital electrode 42 and it is not necessary to make the nozzle diameter small, such aforementioned reliability issues in the aforementioned prior methods may be neglected.
However, in this configuration, since the parallel interdigital electrode is utilized, the generated surface acoustic waves tend to propagate in an unintended direction to cause relatively low energy efficiency, crosstalk and unstable jetting direction or unstable diameter of the produced ink droplet compared to the aforementioned other prior art methods. In order to enhance a directivity of the propagation of the surface acoustic wave, the width d of the interdigital electrodes have to be not less than 10 times the wavelength .lambda. of the generated surface acoustic wave. In addition, the diameter of the ink droplet is affected directly by the width d of the interdigital electrode, the wavelength .lambda. must be much shorter in order to generate a much smaller ink droplet. However, since the shortening of the wavelength directly induces the increasing of the oscillating frequency, an expensive high frequency power supply may be needed; therefore, the oscillating frequency can not be increased so easily.
The disclosures of the following documents also relate to the present invention.
JP-A 62-251153 discloses a surface acoustic wave generator comprising a longitudinal acoustic horn for containing a liquid ink, plural piezoelectric elements that are activated at once to generate standing surface acoustic waves on a free surface of the ink and plural addressing elements for addressing respective wave fronts of the standing surface acoustic wave, wherein both piezoelectric elements and addressing elements are submerged in ink.
JP-A 62-264962 discloses a surface acoustic wave controller for a nozzleless ink droplet ejector comprising an ink pool, plural energy transducers submerged in ink for generating surface acoustic waves each having an energy less than the threshold level sufficient to jet an ink droplet at a certain concentrated point of energy and plural control electrodes located near the concentrated point of energy of a respective wave under a free surface of ink for providing additional energy to jet the ink droplet therefrom.
JP-A 2-172748 discloses a slit-jet printer head comprising a longitudinal ink tank, a first vibrating member located at a side portion of the ink tank for generating meniscuses of the ink due to a generated standing surface wave and a second vibrating member located at a bottom of the ink tank corresponding to each meniscus for providing additional energy to each meniscus to jet an ink droplet therefrom.
JP-A 2-178056 discloses a slit-jet printer head comprising the same features as those of JP-A 2-172748 and further comprising a controller for controlling a frequency applied to ink by the first vibrating means for adjusting relative position between each meniscus and respective second vibrating member.